[en] We present in this work a method for fluid flow visualization in a system using radioactive tracers. The method is based on single photon emission computed tomography techniques, applied to a limited number of discrete detectors. We propose in this work a method for the estimation of the transport matrix of photons, associated to the acquisition system. This method is based on the modelization of profiles acquired for a set of point sources located in the imaged volume. Monte Carlo simulations allow to separate scattered photons from those directly collected by the system. The influence of the energy tracer is exposed. The reconstruction method is based on the maximum likelihood - expectation maximization algorithm. An experimental device, based on 36 detectors was realised for the visualization of water circulation in a vessel. A video monitoring allows to visualize the dye water tracer. Dye and radioactive tracers are injected simultaneously in a water flow circulating in the vessel. Reconstructed and video images are compared. Quantitative and qualitative analysis show that fluid flow visualization is feasible with a limited number of detectors. This method can be applied for system involving circulations of fluids. (author)

[en] The purpose of this experimental study was to analyze a two-dimensional cavitating shear layer. The global aim of this work was to obtain a better understanding and modeling of cavitation phenomenon in a 2D turbulent sheared flow which can be considered as quite representative of cavitating rocket engine turbopomp inducers. This 2D mixing layer flow provided us a well documented test case which can be used for the characterization of the cavitation effects in sheared flows. The development of a velocity gradient was observed inside a liquid water flow: Kelvin-Helmholtz instabilities developed at the interface. Vaporizations and implosions of cavitating structures inside the vortices were observed. X-ray attenuation measurements were performed to estimate the amount of vapor present inside the mixing area. Instantaneous two-dimensional void ratio fields were acquired. The real spatial resolutions are 0.5 mm with 2000 fps and 1.5 mm with 20 000 fps. The effective time resolution is equal to the camera frame rate up to a 19% void ratio variation between two consecutive images. This seems to be sufficient in the context of the present flow configuration. The two-phase structures present inside the mixing area were analyzed at three different cavitation levels and their behaviors were compared to non-cavitating flow dynamic. Convection velocities and vortices shedding frequencies were estimated. Results show that vapor was transported by the turbulent velocity field. Statistical analysis of the void ratio signal was carried out up to the fourth order moment. This study provided a global understanding of the cavitating structure evolution and of the cavitation effects on turbulent sheared flows.

[en] The objective of the paper is to present characterization tools for specific metallic foams objects. As a first step, the objective is to obtain the geometric model of the foam as an input for computed fluid dynamics code. In a second stage, the water behavior in foam samples is studied in free conditions. To address these objectives, an X-ray microtomograph system based on a microfocus X-ray generator and the Medipix2 detector has been implemented. Such X-ray generator has a focal spot size in the magnitude of 1 μm that allows a geometric magnification of the sample without blurring images. Experimental constraints are details to observe in the foams in the magnitude of a few tens of micrometers or less, which implies very low contrast. For these reasons the Medipix2 detector is well suited as a very low noise detector. Two-dimensional images are acquired for 360 projections of the foam. The three-dimensional image is obtained by using an algebraic algorithm Ordered Subset Expectation Maximization (OSEM). Two spatial scales are studied in dry and wet conditions for the foams. Images acquired on a 10 mm² sample of foam with pixel size equal to 50 μm are used to make the analysis at a macroscopic scale of geometry and water kinetics. Images acquired on a 1 mm² sample of foam with pixel sizes equal to 5 μm are used for a thin characterization of the geometry and to reconstruct the water distribution along the struts of the foam

[en] Oral presentations addressed the use of X rays and materials of the nuclear industry (contribution of X rays to the study of nuclear fuels, contribution of X ray diffraction to the study of the behaviour of cement materials under γ and electronic irradiation, complementarity between X ray diffraction and absorption to understand precipitation phenomena during nuclear fuel recycling, evolution of internal stresses generated within a Zr alloy oxidised at high temperature and then cooled, study of the quantitative precipitation of the uranyl ion by organic ligands, development of the MARS line for the study of structural properties of radioactive solids and liquids through a combined use of X ray diffraction and absorption), low energy and spectroscopy, fluorescence X and chemical profilometry, small and wide angle scattering, relationships between structure and properties, microstructure and texture and stresses, thin layers and interfaces, tomography, instrumentation (new sensors and new practices), contributions of general interest

[en] The Societe Hydrotechnique de France (SHF) and the International Association for Hydraulics Research (IAHR) are organizing a two-day seminar related to the advances on two-phase flow modeling, in Lyons, France on Nov. 25-26, 2004. The objectives of this meeting are to bring together French and also European engineers, scientists and academics to discuss the new needs generated by the use of 'small scale' two-phase CFD technology. Several Research Institutes are involved in long-term research programs aimed at developing a new generation of CFD tools and models for two-phase flow and heat transfer modeling. It has always been the continuous role of SHF to put into contact 'problems' with 'solutions' and to animate the French/European fluid mechanics and Hydraulics community by offering meeting opportunities. By organizing this meeting, SHF has primarily four main objectives. 1. To provide a tribune to industry to present to our colleagues of academia and other research institutes existing industrial projects on two-phase CFD, at CEA, Electricite de France and Total for example. These projects involve a refined modeling effort towards multiphase 3D time-averaged modeling of two-phase flow and quasi 'direct simulation'. 2. Since the end of the CNRS-GDR 'Gredic' in 2000 (Groupement de recherches sur les ecoulements diphasiques), which was exceptionally successful (8 years long) and chaired by Professor Jean-Marc Delhaye of CEA/Ecole Centrale Paris and Clemson University, SC, USA, the French two-phase flow 'club' is missing some animation on a regular basis. This meeting may become an opportunity to revive this era. 3. To promote some real technical exchanges between the SHF and AIRH members who usually pertain to slightly disconnected communities but do have common technical issues. 4. To help identifying the research needs in these aforementioned areas in the different disciplines upon which a sound physical model is based and validated, i.e. physical modeling, advanced instrumentation development, numerical, and experimental techniques. This scope is of course very wide and the focus is put on studies consistent with the scales relevant to the 3D models or DNS. This document gathers the abstracts of all presentations given at this meeting. INIS-relevant presentations are presented in separate records (RN: 38013694 to 38013705).